Lrexlib 2.2 Reference Manual

Table of Contents

Introduction

Lrexlib provides bindings of the two principal regular expression library interfaces (POSIX and PCRE) to Lua 5.1.

Lrexlib builds into shared libraries called by default rex_posix.so and rex_pcre.so, which can be used with require.

Lrexlib is copyright Reuben Thomas 2000-2007 and copyright Shmuel Zeigerman 2004-2007, and is released under the MIT license.

Notes

  1. Most functions and methods in Lrexlib have mandatory and optional arguments. There are no dependencies between arguments in Lrexlib's functions and methods. Any optional argument can be supplied as nil (or omitted if it is trailing one), the library will then use the default value for that argument.

  2. This document uses the following syntax for optional arguments: they are bracketed separately, and commas are left outside brackets, e.g.:

    MyFunc (arg1, arg2, [arg3], [arg4])

  3. Throughout this document, the identifier rex is used in place of either rex_posix or rex_pcre, that are the default namespaces for the corresponding libraries.

  4. All functions receiving a regular expression pattern as an argument will generate an error if that pattern is found invalid by the used POSIX / PCRE library.

  1. The default value for compilation flags (cf) that Lrexlib uses when the parameter is not supplied or nil, is:

    • 0 for PCRE
    • REG_EXTENDED for POSIX regex library

    For PCRE, cf may also be supplied as a string, whose characters stand for PCRE compilation flags. Combinations of the following characters (case sensitive) are supported:

    Character

    PCRE flag

    i

    PCRE_CASELESS

    m

    PCRE_MULTILINE

    s

    PCRE_DOTALL

    x

    PCRE_EXTENDED

    U

    PCRE_UNGREEDY

    X

    PCRE_EXTRA

  1. The default value for execution flags (ef) that Lrexlib uses when the parameter is not supplied or nil, is:

    • 0 for PCRE
    • 0 for standard POSIX regex library
    • REG_STARTEND for those POSIX regex libraries that support it, e.g. Spencer's.
  1. Parameter locale (lo) can be either a string (e.g., "French_France.1252"), or a userdata obtained from a call to maketables. The default value, used when the parameter is not supplied or nil, is the built-in PCRE set of character tables.

Common (PCRE and POSIX) functions and methods

match

rex.match (subj, patt, [init], [cf], [ef], [lo])

The function searches for the first match of the regexp patt in the string subj, starting from offset init, subject to flags cf and ef.

PCRE: A locale lo may be specified.

Parameter Description Type Default Value
subj subject string n/a
patt regular expression pattern string n/a
[init] start offset in the subject (can be negative) number 1
[cf] compilation flags (bitwise OR) number cf
[ef] execution flags (bitwise OR) number ef
[lo] [PCRE] locale string or userdata locale
Returns on success:
  1. All substring matches ("captures"), in the order they appear in the pattern. false is returned for sub-patterns that did not participate in the match. If the pattern specified no captures then the whole matched substring is returned.
Returns on failure:
  1. nil

find

rex.find (subj, patt, [init], [cf], [ef], [lo])

The function searches for the first match of the regexp patt in the string subj, starting from offset init, subject to flags cf and ef.

PCRE: A locale lo may be specified.

Parameter Description Type Default Value
subj subject string n/a
patt regular expression pattern string n/a
[init] start offset in the subject (can be negative) number 1
[cf] compilation flags (bitwise OR) number cf
[ef] execution flags (bitwise OR) number ef
[lo] [PCRE] locale string or userdata locale
Returns on success:
  1. The start point of the match (a number).
  2. The end point of the match (a number).
  3. All substring matches ("captures"), in the order they appear in the pattern. false is returned for sub-patterns that did not participate in the match.
Returns on failure:
  1. nil

gmatch

rex.gmatch (subj, patt, [cf], [ef], [lo])

The function is intended for use in the generic for Lua construct. It returns an iterator for repeated matching of the pattern patt in the string subj, subject to flags cf and ef.

PCRE: A locale lo may be specified.

Parameter Description Type Default Value
subj subject string n/a
patt regular expression pattern string n/a
[cf] compilation flags (bitwise OR) number cf
[ef] execution flags (bitwise OR) number ef
[lo] [PCRE] locale string or userdata locale

The iterator function is called by Lua. On every iteration (that is, on every match), it returns all captures in the order they appear in the pattern (or the entire match if the pattern specified no captures). The iteration will continue till the subject fails to match.

gsub

rex.gsub (subj, patt, repl, [n], [cf], [ef], [lo])

This function searches for all matches of the pattern patt in the string subj and replaces them according to the parameters repl and n (see details below).

PCRE: A locale lo may be specified.

Parameter Description Type Default Value
subj subject string n/a
patt regular expression pattern string n/a
repl substitution source string, function or table n/a
[n] maximum number of matches to search for, or control function, or nil number or function nil
[cf] compilation flags (bitwise OR) number cf
[ef] execution flags (bitwise OR) number ef
[lo] [PCRE] locale string or userdata locale
Returns:
  1. The subject string with the substitutions made.
  2. Number of matches found.
  3. Number of substitutions made.
Details:

The parameter repl can be either a string, a function or a table. On each match made, it is converted into a value repl_out that may be used for the replacement.

repl_out is generated differently depending on the type of repl:

  1. If repl is a string then it is treated as a template for substitution, where the %X occurences in repl are handled in a special way, depending on the value of the character X:
  • if X represents a digit, then each %X occurence is substituted by the value of the X-th submatch (capture), with the following cases handled specially:
    • each %0 is substituted by the entire match
    • if the pattern contains no captures, then each %1 is substituted by the entire match
    • any other %X where X is greater than the number of captures in the pattern will generate an error ("invalid capture index")
    • if the pattern does contain a capture with number X but that capture didn't participate in the match, then %X is substituted by an empty string
  • if X is any non-digit character then %X is substituted by X

All parts of repl other than %X are copied to repl_out verbatim.

  1. If repl is a function then it is called on each match with the submatches passed as parameters (if there are no submatches then the entire match is passed as the only parameter). repl_out is the return value of the repl call, and is interpreted as follows:
  • if it is a string or a number (coerced to a string), then the replacement value is that string;
  • if it is a nil or a false, then no replacement is to be done;
  1. If repl is a table then repl_out is repl [m1], where m1 is the first submatch (or the entire match if there are no submatches), following the same rules as for the return value of repl call, described in the above paragraph.

Note: Under some circumstances, the value of repl_out may be ignored; see below.

gsub behaves differently depending on the type of n:

  1. If n is a number then it is treated as the maximum number of matches to search for (an omitted or nil value means an unlimited number of matches). On each match, the replacement value is the repl_out string (see above).

  1. If n is a function, then it is called on each match, after repl_out is produced (so if repl is a function, it will be called prior to the n call).

    n receives 3 arguments and returns 2 values. Its arguments are:

    1. The start offset of the match (a number)
    2. The end offset of the match (a number)
    3. repl_out

    The type of its first return controls the replacement produced by gsub for the current match:

    • true -- replace/don't replace, according to repl_out;
    • nil/false -- don't replace;
    • a string (or a number coerced to a string) -- replace by that string;

    The type of its second return controls gsub behavior after the current match is handled:

    • nil/false -- no changes: n will be called on the next match;
    • true -- search for an unlimited number of matches; n will not be called again;
    • a number -- maximum number of matches to search for, beginning from the next match; n will not be called again;

split

rex.split (subj, sep, [cf], [ef], [lo])

The function is intended for use in the generic for Lua construct. It is used for splitting a subject string subj into parts (sections). The sep parameter is a regular expression pattern representing separators between the sections.

The function returns an iterator for repeated matching of the pattern sep in the string subj, subject to flags cf and ef.

PCRE: A locale lo may be specified.

Parameter Description Type Default Value
subj subject string n/a
sep separator (regular expression pattern) string n/a
[cf] compilation flags (bitwise OR) number cf
[ef] execution flags (bitwise OR) number ef
[lo] [PCRE] locale string or userdata locale

On every iteration pass, the iterator returns:

  1. A subject section (can be an empty string), followed by
  2. All captures in the order they appear in the sep pattern (or the entire match if the sep pattern specified no captures). If there is no match (this can occur only in the last iteration), then nothing is returned after the subject section.

The iteration will continue till the end of the subject. Unlike gmatch, there will always be at least one iteration pass, even if there's no matches in the subject.

flags

rex.flags ([tb])

This function returns a table containing numeric values of the constants defined by the used regex library (either PCRE or POSIX). Those constants are keyed by their names (strings). If the table argument tb is supplied then it is used as the output table, else a new table is created.

The constants contained in the returned table can then be used in most functions and methods where compilation flags or execution flags can be specified. They can also be used for comparing with return codes of some functions and methods for determining the reason of failure. For details, see PCRE and POSIX documentation.

Parameter Description Type Default Value
[tb] a table for placing results into table nil
Returns:
  1. A table filled with the results.

new

rex.new (patt, [cf], [lo])

The functions compiles regular expression patt into a regular expression object whose internal representation is correspondent to the library used (PCRE or POSIX regex). The returned result then can be used by the methods tfind, exec and dfa_exec. Regular expression objects are automatically garbage collected.

PCRE: A locale lo may be specified.

Parameter Description Type Default Value
patt regular expression pattern string n/a
[cf] compilation flags (bitwise OR) number cf
[lo] [PCRE] locale string or userdata locale
Returns:
  1. Compiled regular expression (a userdata).

tfind

r:tfind (subj, [init], [ef])

The method searches for the first match of the compiled regexp r in the string subj, starting from offset init, subject to execution flags ef.

Parameter Description Type Default Value
r regex object produced by new userdata n/a
subj subject string n/a
[init] start offset in the subject (can be negative) number 1
[ef] execution flags (bitwise OR) number ef
Returns on success:
  1. The start point of the match (a number).
  2. The end point of the match (a number).
  3. Substring matches ("captures" in Lua terminology) are returned as a third result, in a table. This table contains false in the positions where the corresponding sub-pattern did not participate in the match.
    1. PCRE: if named subpatterns are used then the table also contains substring matches keyed by their correspondent subpattern names (strings).
Returns on failure:
  1. nil
Notes:
  1. If named subpatterns (see PCRE docs) are used then the returned table also contains substring matches keyed by their correspondent subpattern names (strings).

exec

r:exec (subj, [init], [ef])

The method searches for the first match of the compiled regexp r in the string subj, starting from offset init, subject to execution flags ef.

Parameter Description Type Default Value
r regex object produced by new userdata n/a
subj subject string n/a
[init] start offset in the subject (can be negative) number 1
[ef] execution flags (bitwise OR) number ef
Returns on success:
  1. The start point of the first match (a number).
  2. The end point of the first match (a number).
  3. The offsets of substring matches ("captures" in Lua terminology) are returned as a third result, in a table. This table contains false in the positions where the corresponding sub-pattern did not participate in the match.
    1. PCRE: if named subpatterns are used then the table also contains substring matches keyed by their correspondent subpattern names (strings).
Returns on failure:
  1. nil
Example:
If the whole match is at offsets 10,20 and substring matches are at offsets 12,14 and 16,19 then the function returns the following: 10, 20, { 12,14,16,19 }.

PCRE-only functions and methods

dfa_exec

[PCRE 6.0 and later. See pcre_dfa_exec in the PCRE docs.]

r:dfa_exec (subj, [init], [ef], [ovecsize], [wscount])

The method matches a compiled regular expression r against a given subject string subj, using a DFA matching algorithm.

Parameter Description Type Default Value
r regex object produced by new userdata n/a
subj subject string n/a
[init] start offset in the subject (can be negative) number 1
[ef] execution flags (bitwise OR) number ef
[ovecsize] size of the array for result offsets number 100
[wscount] number of elements in the working space array number 50
Returns on success (either full or partial match):
  1. The start point of the matches found (a number).
  2. A table containing the end points of the matches found, the longer matches first.
  3. The return value of the underlying pcre_dfa_exec call (a number).
Returns on failure (no match):
  1. nil
Example:
If there are 3 matches found starting at offset 10 and ending at offsets 15, 20 and 25 then the function returns the following: 10, { 25,20,15 }, 3.

maketables

[PCRE only. See pcre_maketables in the PCRE docs.]

rex.maketables ()

Creates a set of character tables corresponding to the current locale and returns it as a userdata. The returned value can be passed to any Lrexlib function accepting the locale parameter.

config

[PCRE 4.0 and later. See pcre_config in the PCRE docs.]

rex.config ([tb])

This function returns a table containing the values of the configuration parameters used at PCRE library build-time. Those parameters (numbers) are keyed by their names (strings). If the table argument tb is supplied then it is used as the output table, else a new table is created.

Parameter Description Type Default Value
[tb] a table for placing results into table nil
Returns:
  1. A table filled with the results.

version

[PCRE only. See pcre_version in the PCRE docs.]

rex.version ()

This function returns a string containing the version of the used PCRE library and its release date.

Other functions

plainfind

rex.plainfind (subj, patt, [init], [ci])

The function searches for the first match of the string patt in the subject subj, starting from offset init.

  • The string patt is not regular expression, all its characters stand for themselves.
  • Both strings subj and patt can have embedded zeros.
  • The flag ci specifies case-insensitive search (current locale is used).
  • This function uses neither PCRE nor POSIX regex library.
Parameter Description Type Default Value
subj subject string n/a
patt text to find string n/a
[init] start offset in the subject (can be negative) number 1
[ci] case insensitive search boolean false
Returns on success:
  1. The start point of the match (a number).
  2. The end point of the match (a number).
Returns on failure:
  1. nil

Incompatibilities with the Previous Versions

Incompatibilities between the versions 2.0 and 1.19:

  1. Lua 5.1 is required
  2. Functions newPCRE and newPOSIX renamed to new
  3. Functions flagsPCRE and flagsPOSIX renamed to flags
  4. Function versionPCRE renamed to version
  5. Method match renamed to tfind
  6. Method gmatch removed (similar functionality is provided by function gmatch)
  7. Methods tfind and exec: 2 values are returned on failure
  8. (PCRE) exec: the returned table may additionally contain named subpatterns

Incompatibilities between the versions 2.1 and 2.0:

  1. match, find, tfind, exec, dfa_exec: only one value (a nil) is returned when the subject does not match the pattern. Any other failure generates an error.

Incompatibilities between the versions 2.2 and 2.1:

  1. gsub: a special "break" return of repl function is deprecated.
  2. (PCRE) gsub, gmatch: after finding an empty match at the current position, the functions try to find a non-empty match anchored to the same position.
Generated on: 2007-06-18 17:22 UTC.